Move Singleton and related structs to namespace base

chrome/browser/prefs/pref_metrics_service.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 #define CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 
 #include <map>
 #include <string>
 
@@ skipping 11 matching lines @@
 class PrefMetricsService : public KeyedService {
  public:
   explicit PrefMetricsService(Profile* profile);
   ~PrefMetricsService() override;
 
   class Factory : public BrowserContextKeyedServiceFactory {
    public:
     static Factory* GetInstance();
     static PrefMetricsService* GetForProfile(Profile* profile);
    private:
-    friend struct DefaultSingletonTraits<Factory>;
+    friend struct base::DefaultSingletonTraits<Factory>;
 
     Factory();
     ~Factory() override;
 
     // BrowserContextKeyedServiceFactory implementation
     KeyedService* BuildServiceInstanceFor(
         content::BrowserContext* profile) const override;
     bool ServiceIsCreatedWithBrowserContext() const override;
     bool ServiceIsNULLWhileTesting() const override;
     content::BrowserContext* GetBrowserContextToUse(
@@ skipping 41 matching lines @@
   PrefService* local_state_;
 
   scoped_ptr<SyncedPrefChangeRegistrar> synced_pref_change_registrar_;
 
   base::WeakPtrFactory<PrefMetricsService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefMetricsService);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_